An engine is a machine that converts energy into useful work that is used to power other machines, including everything from small appliances to generators and vehicles to heavy machinery. Engines work by extracting energy from fuels. Fuels are any materials that can be burned to release energy. Liquid fuels are commonly used to supply energy. Liquid fuels share certain attributes, such as hydrogen based compounds, including hydrogen and or hydrocarbons. The molecular structure and the amount of hydrocarbons in a liquid fuel affects its properties. For example, gasoline ignites more easily than diesel fuel because gasoline has a lower energy density and is therefore more volatile than diesel fuel; however, gasoline ignites at a higher temperature than diesel fuel because gasoline has a higher octane rating (octane measured relative to a mixture isomers to determine autoignition resistance). A low tendency to autoignite is desirable in a gasoline engine to avoid back firing. Using higher combustion temperatures in an engine results in a faster burn rate, producing more power from a smaller engine. Diesel fuel will, however, deliver more energy than gasoline if given sufficient time to burn because diesel fuel has a higher energy density than gasoline (the energy density of gasoline is about 31.60 MJ/L; diesel is about 35.5; gasoline contains about 150,000 BTU/gal; diesel about 170,000).
To control the burn of a fuel, fuels are typically ignited in a chamber that includes a fuel injector and an exhaust system and provides the ability to control pressure and temperature. A mixture of fuel and air containing oxygen will ignite when the concentration and temperature of reactants are sufficiently high. Alternately, an ignition source or a detonation device may be used to initiate combustion or to detonate the air/fuel mixture. A typical ignition device used in engines is an electrical charge, such as that produced by a spark plug.
A spark plug or other ignition device creates an electrical current that ignites the air/fuel mixture in the combustion chamber. An efficient burn is achieved through the use of proper timing of the spark, the proper heat range, and the appropriate voltage requirements for the given fuel.
After the fuel is ignited, it burns. Combustion is an incomplete burn of the fuel. Incomplete combustion occurs when too little oxygen is supplied for too little time for the fuel to burn completely. The fuel burns, but produces numerous by-products. For example, when a hydrocarbon burns completely, the reaction typically yields carbon dioxide and water. In incomplete combustion, the burn also produces numerous toxic by-products, such as carbon monoxide and nitrogen oxides. Incomplete combustion is a problem because these by-products can be quite unhealthy and damaging to the environment.
On the other hand, the complete burning a fuel—known as detonation—produces minimal by-products. Detonation burns the fuel to its basic components. Detonation is achieved through factors such as the provision of an optimum amount of air, optimum mixing of the air with the fuel, high initial temperatures, and proper design of the combustion chamber. In existing engines, “complete” burning is usually not achieved; even “near complete” fuel burning typically yields minor amounts of by-products.
The burning of a highly caloric fuel generally results in an incomplete burn producing toxic by-products. To control these by-products, existing engines are made to deliberately drop the temperature and pressure in the chamber immediately after combustion starts but before detonation occurs to avoid the stress and heat produced by such a large amount of energy. Existing engines attempt to avoid detonation by exhausting the gases of combustion from the chamber while they are still burning. In so doing, toxic by-products have the potential to enter the environment. Due to pollution standards for motor vehicles in the United States and abroad, additional components, such as catalytic converters, must be added to the exhaust system to remove these toxic by-products.
The main reason for the deliberate release of energy is that standard internal combustion engines are not designed to handle the temperature and pressure necessary for complete detonation. Standard internal combustion, which is somewhat pressurized but not for a sufficient period of time to allow for a complete burn, is inefficient and requires elaborate heat exchangers and catalytic converters to capture lost heat and control pollution. Higher oxidized combustion coupled with elaborate heat exchangers, lubrication systems, cooling systems and the like, can provide energy with less pollution while maintaining a portion of the heat, but such a design increases the cost of the engine.
Not only does the cost of the engine increase because of the additional components, but the typical practice of releasing gases while the fuel is burning in existing engines is very inefficient. The amount of heat that is removed in a typical engine to avoid the production of toxic by-products can reduce the torque of an engine by over 100%. The inefficient deliberate loss of energy causes poor engine performance, so manufacturers resort to higher frequencies of ignitions to increase power. The increase in combustion events results in higher average heat transfer rates from the hot burned gases to the walls of the chamber. These higher temperatures cause thermal stress to a typical engine.
Timing of the introduction of the fuel, ignition, combustion or detonation, exhaust and reintroduction of the cycle are key factors in the efficiency of an engine. Ignition rates are typically based on the type of fuel and the amount of power needed. For example, the burn of a highly caloric fuel, which produces higher flame temperatures in combustion, requires more time between ignitions to decrease the temperature. Ignition rates increase upon the need for additional power and are low when the machine is at rest.
The pressure inside the chamber is in part a factor of ignition rates and exhaust rates. The greater the ignition rate, the higher the pressure in the chamber; the greater the exhaust rate, the lower the pressure in the chamber. Pressure is also related to temperature. As the temperature in the chamber drops, the pressure drops.
To obtain the optimum temperature and pressure necessary to minimize toxic by-products, sensors are added to monitor the fuel burning process. Pressure sensors measure pressure by comparing a reference to the level of charge flow associated with a specific level of pressure. Pressure is dependent upon atmospheric conditions and altitude. Temperature sensors typically used in fuel burning are any type of temperature sensor appropriate for sensing the temperature under such conditions.
In a machine, pressure and temperature sensors are generally used to feed data to a controller, such as a process logic controller (PLC), which in turn controls the pressure, temperature, ignition, and the like. A PLC is a computer designed for monitoring and controlling equipment by accepting signals from the sensors and other sources and applying the data to a set of instructions within its memory.
Many attempts have been made to provide low cost, efficient engines. One example is the steam engine, which uses a fuel to change the state of a liquid (typically, water, but other fluids may be used). Steam engines work by using the heat energy in the fuel to heat the liquid to a high-pressure steam state. When heat is transferred to a liquid, such as water, the water heats and boils and is eventually evaporated or vaporized. The pressure of water when heat is applied in a closed system increases in proportion to the temperature. When water in a sealed tank is heated, pressure builds up.
Water, however, resists vaporizing. Water has a high specific heat capacity and a high heat of vaporization due to the strong inter-molecular hydrogen bonds that must be broken during vaporization. A large amount of energy (about 41 kJ/mol) is required to evaporate water.
Existing engines suffer from the problem of not being able to efficiently generate a sufficient amount of energy to vaporize water without producing harmful by-products. U.S. Pat. No. 4,240,259 to Vincent (“Vincent”) describes a boiler with an external combustion chamber that heats water in a pressure chamber to produce steam. Standard boiler combustion is essentially not pressurized and requires the recapture of heat. For continuous, highly oxidized combustion to be “clean burning” and “pollution free” as described in Vincent, the temperature of the burn must be kept artificially low to prevent nitrogen/oxygen toxic by-product formation. Vincent addresses the heat loss by recovering steam in a steam accumulator. The steam is re-pressurized and used again. Such a design, however increases the cost of the engine and decreases performance.
Another method of increasing the efficiency of the energy used to vaporize water is by using a heat sink to expose larger surface areas of water to the energy. A heat sink is a system capable of absorbing heat from an object with which it is in thermal contact without a phase change or a significant variation in temperature. Where heat is introduced to as much water surface area as possible, the pressure build up occurs more rapidly.
Insulating materials are another method of retaining heat in the creation of large amounts of energy. By using an insulator, energy is conserved to increase operational efficiency and reduce fuel costs. Selecting insulating materials usually depends upon heat resistance and cost. The insulation material can also be coated with a protective covering.
Currently, no low cost engine exists that efficiently burns a fuel without the production of toxic by-products. Accordingly, a need exists for an engine that is optimally designed to burn a fuel without additional components, such as catalytic converters and external re-pressurization devices. A need exists for a highly efficient, low cost engine that extracts energy from a fuel to create an energized fluid that can be used to do work.